GENEVA -- The northern hemisphere has been warming twice as fast as the southern hemisphere in recent years, the U.N's weather agency said Thursday.

In its annual report on the state of the global climate, the World Meteorological Agency said that in the period 1997-2006 the average temperature in the north was 0.53 degrees Celsius (0.95 Fahrenheit) warmer than the average for 1961-1990.

In the south, average temperatures rose by 0.27 degrees Celsius (0.49 Fahrenheit) in the same period, according to the report.

"So far the northern hemisphere is warming much more than the southern hemisphere," WMO expert Omar Baddour told The Associated Press.

He said one reason for the difference was the greater proportion of land to water surface in the north.

"The oceans respond much slower to any change in temperature. This explains why the northern hemisphere, which has more land than the southern hemisphere, got as much as twice the increase in temperature than in the southern hemisphere," Baddour said.

Another factor was a fast-spinning ring of air over the Arctic which affects the jet stream that helps drive the movement of winter storms, he said.

"Part of the explanation comes from the fact that what is called the North Atlantic Oscillation dominates the northern hemisphere, in particular the Atlantic and Europe area," Baddour said.

At the moment this weather effect is contributing to warming in the north, he said, but this could change.

Globally, temperatures have been rising by 0.18 degrees Celsius (0.32 Fahrenheit) each decade for the last thirty years, according to the report.

The effects have been seen in unusually mild winters and autumns, and extreme temperatures during the summer months, WMO said.

Large parts of Europe had their warmest autumn in 2006 since records began, while the thermometer peaked at 44.2 degrees Celsius (111.6 Fahrenheit) in Sydney, Australia, and 44.6 degrees Celsius (112.3 Fahrenheit) in Bom Jesus, Brazil, this year.

Overall, temperatures were 0.42 degrees Celsius (0.76 Fahrenheit) higher in 2006 than during the 1961-1990 period.

The high temperatures have been accompanied by extended droughts in eastern Africa, Australia, the United States and China. Sudden rains that followed the drought in some of these areas have caused flash floods, because the dry ground was unable to absorb water, the report said.

Severe flooding was also recorded in the Philippines, eastern Europe and the New England region of the United States, the report said, but it had yet to be established whether there has been a direct link between the heat and rainfall.

Another benchmark indicator of global weather was the decrease in Arctic sea ice, which is melting at a rate of 8.59 percent each decade. WMO said this meant a loss of some 60,400 sq. kilometers (23,300 sq. miles) of sea ice each year _ an area comparable to the size of the West African country Togo or the U.S. state of West Virginia.